In 1945 a committee of the Department of Agriculture estimated that the probable cost of aerial topdressing alone would be about £4 per ton of fertiliser (on a basis of 2 cwt per acre). Prices charged in the early 1950s were slightly lower than this estimate. Even 10 years later, and in spite of increases in the cost of all essential components, topdressing charges have not increased. The following factors are responsible for this stability during a period when most other services were forced to increase their charges:

1. A greater number of farm airstrips has reduced the distance between airstrip and target. There are now about 10,000 privately owned airstrips.

2. A steady improvement in the quality of the airstrips themselves has led to increases in payloads, less wear and tear of aircraft, and greater safety.

3. New and more efficient aircraft have been introduced.

4. The methods of the mechanical handling of fertilisers have been improved. Fertilisers supplied in bags have been replaced in many instances by fertilisers supplied in bulk, with a speeding up of handling.

5. Fertiliser bulk stores at frequent intervals along railway lines have been constructed, allowing quicker delivery at short call. This development is mainly confined to the North Island.

6. More specialised training programmes have increased the efficiency of pilots. Many of these factors have contributed to a substantial increase in the fertiliser spread per flying hour. A mean of 2·8 tons per flying hour was spread in 1951; in 1958 it was 6·5 tons, and by 1962 it rose to 7·9 tons.

Overall efficiency of the aerial topdressing industry could be further increased by a more evenly distributed demand for aerial topdressing throughout the year. In the years 1960–62 nearly 50 per cent of all fertilisers supplied were spread during four months of the year, from February to May inclusive. In many cases, however, autumn topdressing may not possess marked advantages over topdressing at other times of the year.